A microelectronic element, such as a semiconductor chip, typically is connected to external circuitry through contacts on the surface of the element. The contacts may be disposed in rows extending along the edges of the chip's front surface. Each such contact may be connected to an external circuit element such as a circuit trace on a supporting substrate or circuit panel.
The rapid evolution of microelectronic elements has created continued demand for incorporation of progressively greater numbers of contacts and leads in a given amount of space.